The Secondary Organs of Plants. 45 



and leaves above ground. As leaves usually live but one 

 season and grow only on stems of that season's growth, so 

 root hairs grow only on young rootlets and last but for a 

 season. They take up water with dissolved mineral matter 

 which goes to the leaves. There it meets carbon -dioxide, 

 which the leaves absorb, and the two are digested or made 

 into starch from which, after being changed into sap, the 

 plant tissues are made. 



Make a drawing of your root, showing, if possible, the 

 bases of- the leaves which grow from it. Where are the 

 rootlets? Make cross and vertical sections. Draw them. 

 Are there any lines of growth ? What do you think caused 

 those lines? What is the nature of the material stored in 

 the root ? What normally becomes of this material ? In 

 what condition would you expect to find the root of a beet 

 or a radish after it had gone to seed ? Why do wild 

 radishes bear more seed than those which are cultivated ? 

 Do these plants turnips, beets, etc. have as large roots 

 in the wild state as when cultivated ? How does a gardener 

 set about to improve the size, flavor, etc. of any of these roots ? 



EXERCISE 27. 



[Read and discuss in the class. ] 



The Secondary Organs of Plants. You have 

 learned that the primary organs of a flowering plant 

 are stems, leaves, roots, and hairs (see note p. 33). 

 You have also had some evidence of the fact that all 

 the other organs of a plant are modified forms of these 



